Table 2

The orientation angle of a TCR onto a pMHC ligand.

TCR-peptide/MHC complexOrientation angle* (°) MHC class
D10-CA/I-Ak 80 II
2C-dEV8/H-2Kb 45 I
N15-VSV8/H-2Kb 54 I
A6-Tax//HLA-A2 56I
B7-Tax/HLA-A2 70 I
  • * The orientation angle of a TCR on MHC is defined as the angle between two vectors determined for the orientation of the TCR and pMHC, respectively. The vector representing the TCR direction is drawn from the mass center of Vα to the mass center of Vβ. The vector representing the pMHC complex direction is drawn from the NH2-terminal Cα atom to the COOH-terminal Cα atom of the peptide in the case of MHC class I. In the case of MHC class II, the vector is drawn from the P1 residue to the P9 residue of the peptide. Note that in Teng et al. (7), twist and tilt were used for semi-quantitative comparison among different TCR-MHC complexes. Essentially, the twist and tilt angles are two projections of the orientation angle more accurately defined here. Whereas the twist is a top view from the TCR toward the MHC, the tilt is a side view, perpendicular to the bound peptide.